Electrical Properties of Quantum Dot Systems


Quantum dots, also denoted as artifical atoms or zero-dimensional electron systems, are objects where few to many electrons are confined in a small spatial enclosure of mesoscopic size (few tens to few hundreds of nanometers), allowing  a single electron only certain eigenvalues for its energy (‘quantum mechanical particle in a box’).

 

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Locally Probing Quantum Hall Samples

Measuring the Hall resistance on a two-dimensional charge carrier system at low magnetic fields allows determining the charge carrier concentration and the type of charge carrier (electron or hole). However at high magnetic field values (and low temperature), magnetic field intervals appear where the measured value is constant and well described by |RH|= h/ie2.

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Microscopic Picture of the Quantum Hall Effect


Scanning probe microscopy investigating quantum Hall samples has been performed in our group for many years and has led to a microscopic picture for the current distribution in quantum Hall samples which contradicts the current-carrying edge-state model.

 

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Current Distribution in the Fractional Quantum Hall Regime


Recently, by using a scanning single-electron transistor microscope, we have measured the evolution of the Hall potential distribution versus magnetic field for several fractional quantum Hall regimes at temperature below 50 milliKelvin.

 

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Magneto-Transport Measurements on Quantum Hall Samples


In recent years we have done conventional magneto-transport measurements on various Hall bar samples demonstrating fingerprints of the edge- and bulk-dominated quantum Hall regime, confirming our microscopic picture which is based on dissipationless current flow in incompressible regions of the two-dimensional electron system.

 

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Single-Electron Transistors on a Tip Array


Single-electron transistors are very sensitive electrometers which can easily detect even the presence of an electron or ion charge in its vicinity. We have developed a technique to fabricate a linear array of tips where on each tip a metal single-electron transistor is located.


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Hall sensors for Scanning Probe Applications


A Hall sensor tip, based on a (Al,Ga)As heterostructure, has been developed for use in a scanning probe microscope operated below 1 Kelvin.


 

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Scanning Probe Microscope operated below 0.1 Kelvin


In the last years, we have developed a scanning probe microscope operated in a 3He-4He dilution refrigerator below 0.1 Kelvin which uses single-electron transistors on a 1D tip array as locally probing electrometers. Hall potential profiles in the integer but also fractional quantum Hall regime have been measured.


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Two-Paths Quantum Hall Devices


Two-paths quantum Hall devices have been discussed in literature in terms of the edge-state picture as electronic interferometers. Our recent experimental investigations on a versatile mesoscopic quantum Hall device with in-situ tunable different combinations of parallel current paths shows in all combinations periodic conductance modulations in the applied magnetic flux.

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Supervelocities in Tunneling?


The transmission time tHa of an incident Gaussian wave packet through a barrier is usually taken as the difference between the time at which the peak of the transmitted packet leaves the barrier of thickness and the time at which the peak of the incident Gaussian wave packet arrives at the barrier. This yields a corresponding transmission velocity cHa = ℓ/tHa which appears under certain conditions as a supervelocity.

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Organic Electronics


The physics of organic solar cells und organic light emitting diodes has been explored in a common work with the company BASF SE in Ludwigshafen, Germany.



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Electron Beam Lithography


Within the Nanostructuring Lab, various substrates – conventional and unconventional – have to be structured by high resolution electron-beam lithography. The density and area size of the written pattern varies from application to application. Diverse resists have to be used, acting either as etching or lift-off mask. Facing a large variety of combinations, we have to challenge electron beam lithography.

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Nanostructuring Lab


With January 1st 2011, the cleanroom facility (previously a facility of the von Klitzing department) became part of the newly established Scientific Facility Nanostructuring Lab. Under class-10 cleanroom conditions with stable room humidity and temperature, samples can be processed by students of the Institute or in service by the cleanroom staff using photolithography, dry and wet etching, and material deposition under vacuum.

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